Numerical and experimental investigation of flow mechanism and application of tandem-impeller for centrifugal compressor

Abstract

The research on tandem impeller technology for centrifugal compressors has not been conducted in a systematic manner and remains incomplete. The lack of insight regarding the flow structure variations between tandem impellers with different meridional flow path profiles is considered to be the primary reason for the confusion. According to a detailed numerical investigation of a series of high-speed compressor stages with different impeller geometries, the secondary flow patterns were analyzed to determine the underlying physics of the impeller flow uniformity improvement, which is the main potential advantage of the tandem method. The impeller inlet/outlet radius ratio D1t/D2 is critical to producing a superior tandem impeller application. The optimum D1t/D2 range of 0.65–0.75 provided the maximum compressor efficiency gain of 1.5% due to the appropriate rearrangement of the impeller flow pattern. Outside of this optimum range, the impeller discharge flow uniformity could not be improved obviously and may even be reduced. The experimental results that were obtained by using centrifugal compressors with and without tandem impellers within the optimum D1t/D2 range further demonstrate the performance gains achieved using the tandem impeller method. This study provides a valuable reference for tandem impeller technology applications and future advanced centrifugal compressor designs.